1. Field of the Invention
This invention relates to an eye-fundus camera, and more particularly to an ophthalmic instrument for detecting a nictitation i.e., winking of an eye being examined.
2. Description of the Prior Art
In recent years, eye-fundus cameras have been widely used in connection with the prevention of adult diseases. Above all, eye-fundus cameras are often used for group medical examinations and, in group medical examinations, the routine examination is usually practiced in a manner which the fundus of each of the right and left eyes is photographed once, but if the examinee nictitates during photography, the fundus of each of the examinee's eyes cannot be accurately photographed. Particularly, in a non-mydriatic eye-fundus camera, once the photographing light is emitted, the eye being examined effects miosis and therefore cannot be immediately re-photographed and further, the photographer may sometimes overlook the nictitation of the examinee resulting in a great inconvenience. As a nictitation detecting method, there is known a method of comparing the increment of any variation in the reflected light from the fundus of the eye being examined illuminated by the eye fundus illuminating light caused by a nictitation with a reference level and detecting the nictitation, as shown in Japanese Laid-open Patent Application No. 69617/1977. However, the eye fundus illuminating light is not constant from person to person due to the differences in the transmission factor in the eyeball and in the size of the pupil diameter. Accordingly, if this reference level is fixed, the reflected light will be too strong or too weak depending on the magnitude of the quantity of illuminating light and this leads to a problem that the nictitation cannot be detected normally. Further, there is a disadvantage that the photographing light will be emitted if the eye being examined nictitates after the photographer has depressed the photographing switch.